> Joel Reicher wrote:
>
> > 'scuse my naivete, but don't you get very good accuracy if you have
> > a consistent hardware clock, a drift file, and enough time (months?)
> > of using many servers to build up a good value in the file?
>
> No. All it takes is one asymetric link between you and your timeserver
> to through your time off.
I use 11 servers, and ntpd appears to regularly change the system peer
as the servers vary very slightly according to each other. Would I
still be suffering the effect you describe?
> With asymetric links (i.e., upload speed != download speed), X != Y.
> Your time will be reliably skewed either a few ms ahead of or behind of
> true time. This is because an asymetric link consistently transmits
> packets faster in one direction that the other.
Unless the asymmetry is on a `critical' link that *all* my NTP packets
travel along (such as my link to my ISP) I don't have a problem, right?
Furthermore, X would have to be different to Y by a non-negligible amount,
no? So even if the link *was* asymmetric, a very fast link would still
be very accurate.
I know I'm pushing the issue, but I always thought that one of the goals
of NTP was to make timekeeping as accurate as possible *without*
requiring the kind of devices you're talking about, and that it does
this by using servers `democratically'.
Cheers,
- Joel
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